[show abstract][hide abstract] ABSTRACT: Inter-decadal modulation of El Niño–Southern Oscillation (ENSO) teleconnections to tropical Indian Ocean (TIO) is investigated in the coupled general circulation model Climate Forecast System (CFS) using a hundred year integration. The model is able to capture the periodicity of El Niño variability, which is similar to that of the observations. The maximum TIO/north Indian Ocean (NIO) SST warming (during spring following the decay phase of El Niño) associated with El Niño is well captured by the model. Detailed analysis reveals that the surface heat flux variations mainly contribute to the El Niño forced TIO SST variations both in observations and model. However, spring warming is nearly stationary throughout the model integration period, indicating poor inter-decadal El Niño teleconnections. The observations on the other hand displayed maximum SST warming with strong seasonality from epoch to epoch. The model El Niño decay delayed by more than two seasons, results in persistent TIO/NIO SST warming through the following December unlike in the observations. The ocean wave adjustments and persistent westerly wind anomalies over the equatorial Pacific are responsible for late decay of El Niño in the model. Consistent late decay of El Niño, throughout the model integration period (low variance), is mainly responsible for the poor inter-decadal ENSO teleconnections to TIO/NIO. This study deciphers that the model needs to produce El Niño decay phase variability correctly to obtain decadal-modulations in ENSO teleconnection.
[show abstract][hide abstract] ABSTRACT: An Integrated Ground Observational Campaign (IGOC) was conducted at Mahabubnagar - a tropical rural station in the southern peninsular India, under the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) program during the period from July to November 2011. Measured chemical composition and carbonaceous aerosols from PM2.5 samples were used in an aerosol optical model to deduce crucial aerosol optical properties, which were then used in a radiative transfer model for radiative forcing estimations. The model derived aerosol optical depth (AOD at 500nm), varied from 0.13 to 0.76 (mean of 0.40±0.18) whereas Ångström exponent (AE) between 0.10 and 0.65 (mean of 0.33±0.17) suggests relative dominance of coarse particles over the station. On the other hand, single scattering albedo (SSA at 500nm) was found to vary from 0.78 to 0.92 (mean of 0.87±0.04) during the measurement period. The magnitude of absorption Ångström exponent (AAE), varied from 0.83 to 1.33 (mean of 1.10±0.15), suggests mixed type aerosols over the station. Aerosol direct radiative forcing was estimated and found to vary from -8.9 to -49.3Wm(-2) (mean of -27.4±11.8Wm(-2)) at the surface and +9.7 to +44.5Wm(-2) (mean of +21.3±9.4Wm(-2)) in the atmosphere during the course of measurements. The atmospheric forcing was observed to be ~30% higher during October (+29±9Wm(-2)) as compared to August (+21±7Wm(-2)) when the station is mostly influenced by continental polluted aerosols. The result suggests an additional atmospheric heating rate of 0.24Kday(-1) during October, which may be crucial for various boundary layer processes in favorable atmospheric conditions.
Science of The Total Environment 10/2013; 468-469C:1093-1102.
[show abstract][hide abstract] ABSTRACT: a b s t r a c t High resolution winds measured by SOund Detection And Ranging (SODAR) in the atmospheric boundary layer (ABL) over Pune, located on the lee side of the Western Ghats (WG) reveal the presence of Low Level Jet (LLJ) in the atmospheric boundary layer (hereafter called as boundary layer jet, BLJ) during southwest monsoon (June–August) for three consecutive years, viz., 2009, 2010 and 2011. Its prevalence only during the monsoon period, even at monthly scale indicates a possible interconnection to another LLJ, Somali jet, present during this period. An investigation is done to look into the dominant mechanisms those could result in such an occurrence in the lee side of the WG. Baroclinicity, inertial oscillation, upstream topographic blocking and variability of Somali jet are the mechanisms considered. Baroclinicity due to east–west temperature gradient on the leeside to induce thermal wind and inertial oscillation appear to have a little role in LLJ formation. However, Somali jet seems to govern the BLJ on the lee side through its dynamical interaction with the WG causing flow reversal and wave breaking above WG and inducing acceleration of downslope winds. The height and sharpness of Somali jet core on the windward side and its magnitude as well as direction with respect to WG are observed to determine the strength of BLJ on the lee side illustrating the signature of the summer monsoon in the boundary layer over Pune.
Journal of Atmospheric and Solar-Terrestrial Physics 09/2013;
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